fix(email) (#5373) r=@shane-tomlinson
fix(email) (#5373) r=@shane-tomlinson

Making the button match the call-to-action in the heading
mozilla/fxa-content-server,mozilla/fxa-content-server,shane-tomlinson/fxa-content-server,mozilla/fxa-content-server,shane-tomlinson/fxa-content-server,shane-tomlinson/fxa-content-server